Yes, you can.
Elpress krf/ksf copper connectors are designed to work with stranded (IEC 60228 class 2) and flexible cables (IEC 60228 class 5). However, when crimping with the elpress tool, pressing out the air will eliminate the differences in the physical area. Therefore, the "gap" initially seen by the operator is an optical problem - it may seem strange, but it is reasonable!